Pulvurized fuel burner



K. K. NAHIGYAN PULVERIZED FUEL BURNER May 16, 1939.

Fled'June 24, 1937 Kava/2K K. NAHIGYAN Patented May 16, 1939 UNiTE STAES ieiENT OFFIQE PULVERIZED FUEL BURNER.

Application June Z4, 1937, Serial No. 150,156

5 Claims.

This invention relates to pulverized fuel burners, and more particularly to burners of the type having a central nozzle to discharge a stream of fuel mixed with primary air and means to supply secondary air to the issuing fuel stream.

Certain diiiiculties are encountered in the operation of prior burners of this type. In some cases the flame of burning fuel impinges on the walls which form the combustion chamber, causing erosion and slag deposition thereon. In other cases it is diicult to maintain ignition of the fuel, particularly when operating at low rates of combustion. In still other cases deposits of coke form on the refractory material which surrounds the burner opening.

It is accordingly one object of the invention to provide a pulverized fuel burner which will produce a very short and compact flame and thereby prevent impingement of the flame on the furnace walls.

It is a further object of the invention to provide a pulverized fuel burner which will remain ignited at very low combustion rates,

It is a still further object of the invention to provide a pulverized fuel burner which will operate without depositing coke on the refractory surfaces of the burner opening.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

In accordance with my invention in its preferred form, I provide a central nozzle arranged to discharge a stream of pulverized fuel and primary air, and I provide means to supply secondary air in surrounding relation to the issuing fuel stream. A central supporting member or hub is mounted within the nozzle near the discharge end thereof, and this hub supports a series of vanes which extend outwardly therefrom across the path of the fuel, each vane being positioned at an angle to the axis of the nozzle so that a Whirl is imparted to the fuel. The outer ends of these vanes are preferably advanced circumferentially in the direction of whirl with respect to the inner ends of the vanes. An annular frusto-conical shroud is preferably secured to the outer ends of the vanes with its larger end toward the on-coming fuel stream and within the fuel nozzle. This shroud is preferably spaced from the central hub in the direction of fuel travel, and the vanes preferably form a frusto-conical structure which flares outwardly in the direction of fuel travel.

(Cl. Mil-104) Referring to the drawing illustrating one embodiment of the invention, and in which like reference numerals indicate like parts,

Fig. l is a somewhat diagrammatic longitudinal section through a pulverized fuel burner;

Fig. 2 is an end view of the fuel nozzle and fuel delector;

Fig. 3 is a section on the line 3-3 of Fig. 2; and

Fig. el. is a View similar to Fig. 3 but showing the m fuel deflector in elevation.

The embodiment illustrated comprises a vertical furnace wall Ill of refractory material having a burner opening II extending therethrough. A

horizontal cylindrical pipe or nozzle I2 is mounted 1 in front of the opening II, the front end of this a The admission of air to the casing Iii may be con- 25 trolled by means of dampers Il.

At the rear or discharge end of the nozzle I2 there is provided a fuel deflector comprising a series of thin flat vanes I9 each of which is positioned at an angle to the axis of the nozzle in order that a whirl may be imparted to the fuel. The inner ends of the vanes are welded 0r otherwise secured to a central annular hub 26 which is attached by means of set-screws 2 I to the rear end of a tube 23 coaxial with the nozzle l2. 23 is slidably supported in the head I4, and a handle 24 is secured to the front end of the tube to facilitate its longitudinal adjustment.

As shown particularly in Fig. 2, the outer ends of the vanes I9 are advanced circumferentially in 40 the direction of fuel whirl with respect to their inner ends, so that the vanes occupy tangential positions. The outer ends of the vanes are welded or otherwise secured to an annular frusto-conical shroud 26 having its larger end toward the oncoming fuel stream and within the fuel nozzle I2, this larger end having a diameter only slightly less than that of the nozzle. The shroud 26 is offset rearwardly in the direction of fuel travel from the 50 inner ends, and adjacent vanes overlap in a cir- 55 A casing I 6 20 The tube 35 cumferential direction throughout their entire lengths.

The operation of the invention will now be apparent from the above disclosure. The stream of pulverized fuel and primary air flows through the receiving head lll, rearwardly through the nozzle I2 and past the vanes i9. The secondary air flows rearwardly from the casing IS and through the opening Il in surrounding relation with the fuel stream. The vanes IB not only whirl the fuel and thereby produce turbulence but they also serve to form a series of jets in each of which the fuel has to a considerable extent separated from the primary air as a result of the pronounced change in the direction of flow. Because of this segregation, each jet has a portion which is very rich in fuel and which therefore ignites very readily. Moreover these jets are directed inwardly by reason of the novel arrangement of the vanes and shroud, so that the secondary air does not have an opportunity to mingle with the jets and dilute their rich fuel portions until after ignition is well started. As a result, ignition can be maintained at unusually low rates of combustion, and when operating at high combustion rates ignition can be obtained so close to the burner that a comparatively small compact flame is produced, thus avoiding impingement of the flame upon the furnace walls. By concentrating the flame close to the burner axis I prevent the fuel particles from contacting with the refractory material surrounding the opening I l, so that coke deposits in this opening are avoided.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A pulver-ized fuel burner comprising a nozzle arranged to discharge a stream of pulverized fuel and primary air, means to supply secondary air around the outside of the fuel stream, a hub mounted within the nozzle near the discharge end thereof, and a series of vanes surrounding the hub with their inner ends secured thereto, each vane extending across the annular space between the hub and the surrounding nozzle and positioned at an angle to the axis of the nozzle so that a whirl is imparted to the fuel stream, the outer ends of the vanes being advanced circumferentially in the direction of whirl with respect to the inner ends of the vanes.

2. A pulverized fuel burner comprising a nozzle arranged to discharge a stream of pulverized fuel and primary air, means to supply secondary air around the outside of the fuel stream, a hub mounted within the nozzle near the discharge end thereof, and a series of vanes surrounding the hub with their inner ends secured thereto, each vane extending across the annular space between the hub and the surrounding nozzle and positioned at an angle to the axis of the nozzle so that a whirl is imparted to the fuel stream, the outer ends of the vanes being advanced circumferentially in the direction of whirl with respect to the inner ends of the vanes, and the vanes being arranged to form a frusto-conical structure which flares outwardly in the direction of fuel travel.

3. A pulverized fuel burner comprising a nozzle arranged to discharge a stream of pulverized fuel and primary air, means to supply secondary air around the outside of the fuel stream, a hub mounted Within the nozzle near the discharge end thereof, a series of vanes surrounding the hub with their inner ends secured thereto, each vane being positioned at an angle to the axis of the nozzle so that a Whirl is imparted to the fuel stream, and an annular frusto-com'cal shroud secured to the outer ends of the vanes Within the nozzle, the shroud converging in the direction of fuel travel.

4. A pulverized fuel burner comprising a nozzle arranged to discharge a stream of pulverized fuel and primary air, means to supply secondary air around the outside of the fuel stream, a hub mounted within the nozzle near the discharge end thereof, a series of vanes surrounding the hub with their inner ends secured thereto, each vane being positioned at an angle to the axis of the nozzle so that a whirl is imparted to the fuel stream, and an annular frusto-conical shroud secured to the outer ends of the vanes With its larger end located within the nozzle and toward the oncoming fuel stream, the shroud being spaced from the central hub in the direction of fuel travel, the vanes forming a frusto-conical structure which flares outwardly in the direction of fuel travel.

5. A pulverized fuel burner comprising a nozzle arranged to discharge a stream of pulverized fuel and primary air, means to supply secondary air around the outside of the fuel stream, a hub mounted within the nozzle near the discharge end thereof, a series of vanes surrounding the hub with their inner ends secured thereto, each vane being positioned at an angle to the axis of the nozzle so that a whirl is imparted to the fuel stream, and an annular frusto-conical shroud secured to the outer ends of the vanes with its larger end located within the nozzle and toward the oncoming fuel stream, the shroud being spaced from the central hub in the direction of fuel travel, the vanes forming a frusto-conical structure which flares outwardly in the direction of fuel travel, and the outer ends of the vanes being advanced circumferentially in the direction of whirl with respect to the inner ends of the vanes.

KEVORK K. NAHIGYAN. 

